The present invention relates to a scroll compressor, and more particularly to an apparatus for adjusting an orbital radius in a scroll compressor, which maintains a distance between centers of a driving shaft and a bushing, thereby determining a radial gap between scroll wraps of a compression chamber to a desired value irrespective of machining and assembling errors.
Referring to FIG. 1, a conventional scroll compressor includes a fixed scroll 1, an orbiting scroll 2, a rotation preventing device 3, and a driving shaft 4. The fixed scroll 1 and orbiting scroll 2 have involute or spiral wraps, respectively. The fixed scroll 1 is fixed to a main frame. The orbiting scroll 2 exhibits an orbital movement by the driving shaft 4 rotated by a motor 5, because the rotation of the orbiting scroll 2 is prevented by the rotation preventing device 3. The orbital movement of the orbiting scroll 2 with respect to the fixed scroll 1 changes the volume of a compression chamber provided therebetween, thereby compressing a refrigerant gas. FIG. 1 also shows a driving pin 4a formed eccentrically at the upper end of the driving shaft 4.
In the conventional scroll compressor, the width of the radial gap between the wrap of the fixed scroll 1 and the wrap of the orbiting scroll 2 is very important. If the gap is too wide, compressed gas will be leaked. On the contrary, if there is no gap, the wraps come into contact with each other and a frictional force between the wraps increases.
As shown in FIGS. 2 and 3, an orbital radius of the orbiting scroll 2, that is, the distance between the center A of the driving shaft 4 and the center C of a bushing 7, is the most important factor to influence the gap between the scroll wraps. The bushing 7 receives the driving pin 4a formed eccentrically at the upper end of the driving shaft 4 and drives the orbiting scroll 2. Generally, if the distance between the center A of the driving shaft 4 and the center C of the bushing 7 is variable, a reliability of the scroll compressor is improved.
When the orbital movement is not performing normally due to an excessive force, for example, due to an obstacle interposed between the scroll wraps or due to attempting to compress a liquid, the bushing 7 moves with respect to the driving pin 4a, thereby increasing the gap between the scroll wraps and consequently moving the orbiting scroll 2 in the same direction. On the contrary, in normal conditions of operation, the bushing 7 moves so as to allow the gap between the scroll wraps to vary in accordance with the centrifugal force of the orbiting scroll 2, the gas pressure of the compression chamber, or the like, to become an optimal minimum value.
Referring to FIGS. 3A and 3B, there is provided a stopper 8' for limiting the relative movement of the bushing 7 with respect to the center B of the driving pin 4a to a predetermined extent. In this situation, when the orbital movement is normal, the distance between the center A of the driving shaft 4 and the center C of the bushing 7, that is, the orbital radius, becomes maximized within the predetermined range, and at the same time the radial gap between the wrap of the fixed scroll 1 and the wrap of the orbiting scroll 2 becomes minimized. On the other hand, when the orbital movement is not within a normal range of positions due to an excessive load (for example, an obstacle is interposed between the scroll wraps or a liquid is to be compressed), the bushing 7 moves so as to allow the distance between the center A of the driving shaft 4 and the center C of the bushing 7 to become narrower, thereby increasing the radial gap between the scroll wraps. At this time, the stopper 8' determines a minimal orbital radius, that is, a maximal gap between the scroll wraps.
As described above, if the minimal radial gap between the scroll wraps is too wide, compressed gas leakage increases. On the contrary, if too narrow, the frictional force between the scroll wraps increases. Therefore, the maximal distance between the center A of the driving shaft 4 and the center C of the bushing 7, (that is, the minimal gap between the scroll wraps) is important.
However, the range of the radial gap cannot be maintained to a designed value because of accumulated errors, for example, machining errors of eccentricity between the center A of the driving shaft 4 and the center B of the driving pin 4a, machining and assembling errors of the inner circumference of the bushing 7 and the outer circumference of the driving pin 4a inserted into the bushing 7, and machining and assembling errors of the stopper 8'.